Flow diverter for controlling the pressure and flow rate in CPAP device

ABSTRACT

A flow diverter valve is used in controlling the pressure and/or flow rate of a breathable gas supplied to the airways of a patient by a breathable gas flow generator supply apparatus during, for example, ventilatory assistance treatments such as non-invasive positive pressure ventilation and nasal Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea. The flow diverter valve includes a vane and a housing. The housing has an inlet port, an outlet port, and an exhaust port. The exhaust port opens to atmosphere, and the inlet port is in fluid communication with the flow generator. The outlet port is in fluid communication with a patient mask via a conduit. The vane is configured with respect to the housing such that a blower associated with the CPAP apparatus remains substantially unchoked, regardless of whether the vane is in the open or closed position.

BACKGROUND OF THE INVENTION

1. Related Art

This application is related to pending U.S. patent application Ser. No.09/598,053 filed on Jun. 21, 2001, describing a control member for avalve and method for determining fluid flow rate through a valve. Thisapplication is also related to U.S. patent application Ser. No.09/642,824 filed on Aug. 22, 2000, describing pressure control in CPAPtreatment or assisted respiration. International PCT Patent ApplicationNo. PCT/AU97/00631 describes varying pressure at a patient mask throughthe period of treatment during inspiration or expiration, andInternational PCT patent application No. PCT/AU96/00586 describes a flowdiverting valve with a rotatable control member, both of which arerelated to this application. The contents of these U.S. andInternational PCT Patent Applications are incorporated herein byreference in their entireties. This application is also related to U.S.Pat. No. 4,944,310, which describes Continuous Positive Airway Pressure(CPAP) treatment, and U.S. Pat. No. 5,245,995 which describesautomatically adjusting nasal CPAP treatment. The contents of thesepatents are incorporated herein by reference in their entireties.

2. Field of the Invention

The present invention relates to a ventilatory assistance apparatus, andin particular, a ventilatory assistance apparatus including a flowdiverter valve in fluid communication with a flow generator.

3. Background of the Invention

Non-Invasive Positive Pressure Ventilation (NIPPV) is a form oftreatment for breathing disorders which can involve a relatively higherpressure of air or other breathable gas being provided to the entranceof a patient's airways via a patient mask during the inspiratory phaseof respiration, and a relatively lower pressure or atmospheric pressurebeing provided in the patient mask during the expiratory phase ofrespiration. In other NIPPV modes the pressure can be made to vary in acomplex manner throughout the respiratory cycle. For example, thepressure at the mask during inspiration or expiration can be variedthrough the period of treatment.

Continuous Positive Airway Pressure (CPAP) treatment is commonly used totreat breathing disorders including Obstructive Sleep Apnea (OSA). CPAPtreatment continuously provides pressurized air or other breathable gasto the entrance of a patient's airways via a patient mask at a pressureelevated above atmospheric pressure, typically in the range 3-20 cm H₂O.CPAP treatment can act as a pneumatic splint of a patient's upperairway.

CPAP treatment can be in a number of forms, including the maintenance ofa constant treatment pressure level, alternating between two differentconstant levels in synchronism with the inspiratory and expiratoryphases of respiration (“bi-level CPAP”), and having an automaticallyadjustable and/or a computer controlled level in accordance with apatient's therapeutic needs. In all of these cases there is a need forcontrol over the pressure of air or breathable gas supplied to thepatient mask.

Breathable gas supply apparatus used in CPAP and NIPPV treatmentsbroadly comprise a flow generator constituted by a continuous source ofair or other breathable gas generally in the form of a blower driven byan electric motor. A pressurized supply of air or other breathable gascan also be used. The gas supply is connected to a conduit or tube,which is in turn connected to a patient mask (or nasal prong) whichincorporates, or has in close proximity, a vent to atmosphere forexhausting exhaled gases, such as carbon dioxide. To vary the flowsupplied to the patient during inspiration and expiration, a valvemember can be used, such as the valve member disclosed in U.S. patentapplication Ser. No. 09/598,053. For example, a cammed rotatable membercan be used to permit a large flow during patient inspiration, and arelatively small (or substantively no) flow during patient expiration.However, this type of valve arrangement may be disadvantageous sinceduring the patient expiration, when the valve member does not permit asignificant, if any flow, the blower, which is upstream of the valvemember, may be choked. Stated differently, flow through and from theblower may temporarily stop if the valve member is positioned to preventor substantially prevent flow to the patient, e.g., when the patient isin the expiration phase of the breathing cycle. When inspiration resumesand the valve member rotates so as to permit flow or more flow to thepatient, the fan or impeller associated with the blower may require afew revolutions (e.g., two) in order to reinstate flow through theimpeller to the conduit and to the patient. As such, the response timeof the CPAP apparatus when changing from the expiration to theinspiration may be delayed.

Treatment pressure of the air or other breathable gas can be controlledby speed control of the electric motor driving the blower of the flowgenerator. An example of a related art flow generator using a speedcontrolled blower is illustrated in FIG. 1. Conventional flow generator110 is comprised by a chamber 112 that is segregated from a housing 114of the flow generator 110. The housing 114 houses control circuitry (notshown) associated with the flow generator 110. The flow generator 110 isfurther comprised by a motor 116 driving an induced flow centrifugalturbine (impeller) 118, which induces the flow of air or breathable gasby an air inlet 120 to pass the air or breathable gas under pressure byan air outlet 122 to the air delivery tube (not shown) and so to themask (also not shown). The turbine 118 has radially directed impellerblades 124. The alternate use of axial fans is known also in CPAPapparatus.

For typical CPAP treatment, the blower motor must be able to change itsoperational speed quickly. This results in the need to supply additionalelectrical power during times of operational speed increases.Disadvantages associated with rapid transitions in motor speed are, forexample, noise, vibration, blower choking, and increased thermaldissipation requirements, in addition to increased power requirements.

Treatment pressure can alternatively be controlled by driving theelectric motor of the blower at a constant speed, and venting orbleeding-off excess air from the output side of the blower. An exampleof this type of related art pressure control is shown in FIG. 2. Aturbine 118 is connected to a plenum chamber 130 by a supply pipe 132.The plenum chamber 130 has a controllable spill valve 134 operable toindexingly open and close an opening 136 in the chamber wall to allowthe venting of air to atmosphere so as to achieve the desired outputpressure at an air outlet 138. Consequently, venting can be associatedwith excessive noise when the treatment pressure is adjusted.Additionally, it is difficult to maintain precise treatment pressureregulation and to maintain a high maximum flow rate, due in part to thelarge volume of plenum chamber 130. Imprecise treatment pressureregulation can lead to patient discomfort.

FIGS. 3A and 3B illustrate a prior art treatment pressure control usinga bleeding valve 140 in fluid communication with blower 150 that isoperated by a mechanism 142 situated within the flow path 144. In thisembodiment, the mechanism 142 operates primarily in either an openposition 146 (FIG. 3A) or a closed position 148 (FIG. 3B), resulting inimprecise, abrupt treatment pressure regulation. Additionally, themechanism 142 situated in the flow path 144 can impede flow and causenoise, and can introduce into the flow path 144 odors and/or othercontaminants generated during the operation of the mechanism 142. Thisresults in patient discomfort and decreased patient compliance withtreatment.

Noise and/or patient discomfort decrease patient compliance withtreatment of breathing disorders. Therefore, there is a need in theprior art for an improved apparatus that increases patient compliancewith treatment by reducing disadvantages including noise emissions andimprecise treatment pressure regulation. There is also a need to providea valve arrangement that can prevent choking of the blower and/orimprove the speed and/or response time when the ventilation changes fromthe expiration mode to the inspiration mode.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide an improved flowdiverter valve and, in a preferred form, a flow diverter valve withreduced noise and/or flow fluctuations and/or increased response speed.

It is another aspect to provide a valve assembly including a flowdiverter vane that does not choke a blower with which it is associated,regardless of the position of the vane.

According to one preferred embodiment, there is provided a valveassembly for use in a ventilator, the valve assembly comprising ahousing and a rotatable vane for directing the flow of air within thehousing. The housing has an inlet port for receiving a flow ofpressurized air from a blower, an outlet port for delivering air to apatient interface and an exhaust port. The vane is rotatable between afirst angular position and a second angular position without choking theblower. In the first angular position, substantially all of the flow ofair received at the inlet port is directed by the vane to the exhaustport. In the second angular position, substantially all of the flow ofair received at the inlet port is directed by the vane to the outletport. In angular positions intermediate of the first and second angularpositions, a fraction of the flow of air received at the inlet port isdirected by the vane to the exhaust port and the complementary fractionof the flow of air received at the inlet port is directed by the vane tothe outlet port.

According to another embodiment, there is provided a ventilatoryassistance apparatus comprising a flow generator and a flow divertervalve, in communication with the flow generator, including a housingdefining an inlet port, an outlet port and an exhaust port. The exhaustport is positioned between the inlet port and the outlet port and isconfigured to exhaust at least one of flow from the inlet port and backflow from the outlet port. A vane moveable between an open position anda closed position can selectively protrude into the flow from the inletport and thereby variably divert the flow from the inlet port to atleast one of the exhaust port and the outlet port. The vane forms aportion of a passage leading to the outlet port when in the closedposition.

In another embodiment, a flow diverter valve comprises a housingdefining an inlet port and an outlet port, an exhaust port positionedbetween the inlet and outlet ports, and a vane moveable between an openposition and a closed position. The vane can selectively protrude intothe flow from the inlet port and thereby variably divert the flow fromthe inlet port to at least one of the exhaust port and the outlet port.The vane forms a portion of a passage leading to the outlet port when inthe closed position.

In yet another embodiment, there is provided a CPAP apparatus comprisinga flow generator and a flow diverter valve, in communication with theflow generator, including a housing defining an inlet port, an outletport and an exhaust port. The exhaust port is positioned between theinlet port and the outlet port and is configured to exhaust at least oneof flow from the inlet port and back flow from the outlet port. A vanemoveable between an open position and a closed position can selectivelyadmit undiverted flow from the inlet port to at least one of the exhaustport and the outlet port when the vane is in the open position.

In yet another embodiment, a flow diverter valve comprises a housingdefining an inlet port and an outlet port, an exhaust port positionedbetween the inlet and outlet ports. A vane moveable between an openposition and a closed position can selectively admit undiverted flowfrom the inlet port to at least one of the exhaust port and the outletport when the vane is in the open position.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be described in orapparent from the following detailed description of preferredembodiments, wherein:

FIG. 1 is a side view of a controllable, variable flow generator in therelated art;

FIG. 2 is a side view of a controllable flow generator in the relatedart;

FIGS. 3A and 3B are side views of a controllable flow generator in theprior art;

FIG. 4 is a top view of a ventilatory assistance apparatus according toan embodiment of the present invention;

FIG. 5 is a perspective view of a ventilatory assistance apparatusaccording to an embodiment of the present invention;

FIG. 6 is a top view showing the vane of FIGS. 4-5 in greater detail;

FIG. 7 is a top view showing additional details of the vane of FIG. 6;

FIG. 8 is a top view showing the housing of FIGS. 4-5 in greater detail;

FIG. 9 is a top view showing the interior of the housing of FIG. 8 ingreater detail;

FIG. 10 is a top view showing additional details of the housing interiorof FIG. 9;

FIG. 11 is a perspective view showing additional details of the housingof FIGS. 4-5;

FIG. 12 is a perspective view showing additional details of the housingof FIGS. 4-5;

FIG. 13 is a perspective view of the flow diverter valve of FIGS. 4-5,illustrating an intermediate position;

FIG. 14 is a top view of a flow diverter valve illustrating an open,venting, Expiratory Positive Airway Pressure (EPAP) position accordingto an embodiment of the present invention;

FIG. 14A is a detailed view of a portion of FIG. 14;

FIG. 15 is a top view of the flow diverter valve of FIG. 5 illustratinga closed, Inspiratory Positive Airway Pressure (IPAP) position;

FIG. 16 is a top view of the flow diverter valve of FIG. 5, illustratingan intermediate position;

FIG. 17 is a top view of a flow diverter valve illustrating an open,venting, Expiratory Positive Airway Pressure (EPAP) position accordingto another embodiment of the present invention;

FIG. 18 is a top view of the flow diverter valve of FIG. 17,illustrating a closed, Inspiratory Positive Airway Pressure (IPAP)position;

FIG. 19 is a top view of the flow diverter valve of FIG. 17,illustrating an intermediate position; and

FIG. 20 is a top view of a flow diverter valve according to yet anotherembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A ventilatory assistance apparatus 11 according to an embodiment of thepresent invention is illustrated in FIG. 4. A flow generator 22, influid communication with a flow diverter valve 12 via an inlet port 16,provides a flow of air or breathable gas to the flow diverter valve 12at a generally constant pressure, typically consistent with a maximumtreatment pressure. Flow diverter valve 12 includes a vane 10 pivotablymounted within the flow diverter valve 12. Pressure and flow rate of theflow of air or breathable gas from the flow generator 22 are controlledby the flow diverter valve 12 and the vane 10. The flow diverter valve12 is connected via an outlet port 18 in fluid communication with a flowmeter 50, although alternate embodiments could incorporate the flowmeter 50 integrally with the flow diverter valve 12. The flow meter 50is connected in fluid communication with a patient mask 54 via a conduit52. The flow generator 22, flow diverter valve 12, and flow meter 50 areenclosed within an apparatus body 56. The apparatus body 56 includes aside wall 98 with an apparatus body opening 96.

FIG. 5 shows a perspective view of the ventilatory assistance apparatus11 shown in FIG. 4. A rotary actuator 58 is shown mounted to the flowdiverter valve 12. In the illustrated embodiment of FIGS. 4-5, the flowmeter 50 is arranged within the apparatus body 56 downstream from theflow generator 22 and the flow diverter valve 12, so that turbulence andflow fluctuations within the flow meter 50 generated by the flowgenerator 22 are minimized. It is understood, however, that alternatearrangements or combinations of the flow generator 22, flow divertervalve 12, and flow meter 50 within the apparatus body 56 are possible.

The flow diverter valve 12 can be used in controlling the pressure andflow rate of a breathable gas supplied to the patient mask 54 during,for example, nasal Continuous Positive Airway Pressure (CPAP) treatmentof Obstructive Sleep Apnea (OSA). However, it will be appreciated thatthe invention is not limited to these particular uses and is equallyapplicable to controlling the flow of any fluid (i.e., gas or liquid)passing a valve.

In this specification, any reference to the patient mask 54 is to beunderstood as incorporating a reference to a nasal mask, mouth mask, anasal and mouth mask in combination, full face mask, nasal pillows ornasal prongs, unless otherwise specifically indicated. Any reference toCPAP treatment is to be understood as embracing all of theabove-described forms of ventilatory treatment or assistance. Allreferences to “treatment pressure” include a continuous pressure thatcan vary with time if desired in accordance with treatment needs, andtherefore is not necessarily of a constant level.

FIG. 6 shows the vane 10 of FIGS. 4 and 5 in more detail. A leading vaneedge 28 and a trailing vane edge 30 of the vane 10 are curved concentricwith a vane pivot axis 34. In the illustrated embodiment shown in FIG.6, the vane pivot axis 34 is arranged centrally equidistant between theleading vane edge 28 and the trailing vane edge 30. This arrangementresults in the leading vane edge 28 and the trailing vane edge 30 havingequal radii of curvature about the vane pivot axis 34. Althoughillustrated as having equal radii of curvature of 20 mm, it isunderstood that a broad range of radii of curvature can be used, e.g.,the radii can be different. The vane pivot axis 34 can be arrangednon-equidistant from the leading vane edge 28 and the trailing vane edge30, resulting in unequal radii of curvature of the leading vane edge 28and the trailing vane edge 30 about the vane pivot axis 34.

In the illustrated embodiment, a first side vane surface 60 and a secondside vane surface 62 of the vane 10 have radii of curvature greater thanthe radii of curvature of the leading vane edge 28 and the trailing vaneedge 30. In particular, the first side vane surface 60 has a radius ofcurvature of 120 mm. The second side vane surface 62 has a radius ofcurvature of 200 mm. Alternatively, other radii can be used including arange of radii of curvature, preferably from between three to four timesthe radii of curvature of the leading vane edge 28 and the trailing vaneedge 30, to radii of curvature of infinity (i.e., side vane surfaces 60and 62 can be flat). The radii of curvature of the first side vanesurface 60 and the second side vane surface 62 can be based on a portionof a National Advisory Committee for Aeronautics (NACA) airfoil sectionfor improved flow characteristics. The convex curvature of the firstside vane surface 60 and the second side vane surface 62 can curveupwards or downwards, or one surface can curve upwards and the otherdownwards, at least depending upon the desired aerodynamiccharacteristics. However, as shown in FIGS. 6 and 7, the surfaces 60, 62preferably curve downward to minimize turbulence. As illustrated, theleading vane edge 28 and the trailing vane edge 30 extend along theirrespective radii of curvature until they intersect with the first sidevane surface 60. As measured about the vane pivot axis 34 along theradii of curvature of the leading vane edge 28 and the trailing vaneedge 30, the intersection points describe an arc of approximately160°-210°, but is preferably 185°. Depending upon the particularaerodynamic characteristics desired for the vane 10, and the radii ofcurvature used for the first side vane surface 60 and the second sidevane surface 62, arcs of varying degree can be used. A smaller radius ofcurvature used for the first side vane surface 60 results in a largerarc, and vice versa.

FIG. 7 shows additional details of the vane 10 of FIGS. 4-6. Leadingvane corners 64, defined by the intersections of the leading vane edge28 with the first side vane surface 60 and the second side vane surface62, are rounded. Trailing vane corners 66, defined by the intersectionsof the trailing vane edge 30 with the first side vane surface 60 and thesecond side vane surface 62, are also rounded. The radii of curvaturefor the leading vane corners 64 and trailing vane corners 66 can varydepending on the particular embodiment. As shown in the embodiment ofFIG. 7, the leading vane corners 64 have an approximate radius ofcurvature of 1 mm. The trailing vane corners 66 preferably have anapproximate radius of curvature of 0.5 mm. Radii of curvature of thevane corners 64 and 66 can be determined by the manufacturing methodsand actual width of the particular vane 10. Additionally, radii ofcurvature of the vane corners 64 and 66 can be chosen as large aspossible while not greatly reducing the sealing area of the vane edges28 and 30. Larger radii of curvature of the leading vane corners 64 areparticularly beneficial to improved aerodynamic characteristics. Thedistance between the centers of the radii of curvature for the leadingvane corners 64 can vary as well, although the distance is illustratedin this embodiment as 3.5 mm. Likewise the distance between the centersof the radii of curvature for the trailing vane corners 66 can vary andis illustrated as 2.5 mm. Preferably, a distance is chosen large enoughto provide sufficient sealing area of the vane edges 28 and 30.

The flow diverter valve 12 illustrated in FIGS. 4-5 includes a housing14. The housing 14 is shown in more detail in FIGS. 8-10, illustratedwithout connecting portions 68 as shown in FIGS. 11-16. The inlet port16 is in fluid communication with a housing interior 70, and the outletport 18 is also in fluid communication with the housing interior 70. Anexhaust port 20 in fluid communication with the housing interior 70opens to atmosphere 72 via apparatus body opening 96. The housing 14also includes a housing through hole 74 and a housing bend 32. Thehousing bend 32 is shaped to provide a smooth continuous curve from theinlet port 16 to the outlet port 18.

FIG. 9 illustrates in more detail the housing interior 70 of the housing14 shown in FIG. 8. The housing bend 32 in this illustrated embodimenthas a radius of curvature of 30 mm. A leading housing surface 24 and atrailing housing surface 26 have a radius of curvature of 20 mm,concentric with the housing through hole 74. Accordingly, the radii ofcurvature of the housing surfaces 24 and 26 vary with the width of theexhaust port 20. Likewise, the radii of curvature of the correspondingvane edges 28 and 30 which can seal against the housing surfaces 24 and26 similarly vary with the width of the exhaust port. A housing bendintersection point 76 is defined by the intersection between the radiusof curvature of the leading housing surface 24 and the housing bend 32.The distance between the housing bend 32 and the leading housing surface24 has been chosen such that the angular distance, measured from thehousing through hole 74, between the housing bend-intersection point 76and the leading housing surface 24 is approximately 30°. The angulardistance can be varied depending upon factors including the speed andrange of movement of the rotary actuator 58. In general, a smallerangular distance between the housing bend intersection point 76 and theleading housing surface 24 results in a faster response time for a givenrotary actuator 58 with a given rotary response speed. However, asmaller angular distance between the housing bend intersection point 76and the leading housing surface 24 results in a corresponding greaterpressure drop across an imaginary line passing through the housing bendintersection point 76 and the leading housing surface 24, as compared toa larger angular distance. An outlet port bend 78 has a radius ofcurvature of 2 mm, variably chosen to provide a smooth flow path throughthe housing interior 70 without sharp changes of direction.

FIG. 10 shows various linear dimensions of the housing interior 70 shownin the embodiment of FIGS. 8-9. The inlet port 16 and the outlet port 18have openings 20 mm wide, to accommodate other components (not shown)connected to the inlet port 16 and the outlet port 18, the particularopening sizes not intrinsic to the function of the flow diverter valve12. The width of the inlet port 16 is narrowed by the housing bend 32such that the width is reduced to 12 mm in the housing interior 70. Thedistance between the housing bend intersection point 76 and the housingthrough hole 74 is 20 mm, the distance from the trailing housing surface26 along the exhaust port 20 to the atmosphere 72 is 10 mm, and thedistance from the trailing housing surface 26 to the outlet port 18 is20 mm. The distance from the outlet port 16 to the leading housingsurface 24 is 25 mm. These distances are chosen to provide a smooth flowpath throughout the housing interior 70 without presenting sharp changesof direction.

FIGS. 11-12 show a perspective view of the housing 14 illustrated inFIGS. 8-10, illustrating the connecting portions 68 of housing 14. Thesame radius and dimension measurements of FIGS. 9-10 are shown in FIGS.11-12. Additionally, FIG. 11 shows the height of the housing 14 as 30 mmto provide a sufficient flow path in this particular embodiment. Thethickness of a housing floor 84 of 2 mm was chosen to provide sufficientrigidity in this particular embodiment in the case that the housing 14is constructed out of plastic. FIG. 12 additionally shows an internaldiameter of the connecting portions 68 of 19 mm, and an externaldiameter of the connecting portions 68 of 25 mm, such diametersaccommodating other components (not shown) connected to the connectingportions 68.

The measurements shown in FIGS. 6-7 and 9-12 are not meant to belimiting in scope, and are only shown for the illustration of oneparticular embodiment.

FIG. 13 illustrates the vane 10 pivotably mounted within the housing 14(the housing 14 shown including the connecting portions 68). The vanepivot axis 34 coincides with the housing through hole 74, allowing thevane pivot axis 34 to extend through the housing through hole 74 andprotrude externally from the housing 14. A lower vane edge 80 cansealingly engage against the housing floor 84. The rotary actuator 58mounted externally to the housing floor 84 (see FIG. 5) can rotate thevane pivot axis 34, in turn rotating the vane 10 about the vane pivotaxis 34. A housing cover (not shown) with a housing cover through holecan be sealably mounted to the top surface of housing 14, enclosing thevane 10 within the housing while securing the upper portion of the vanepivot axis 34 via the housing cover through hole. The housing coversealably engages the top surfaces of the housing 14 and an upper vaneedge 82, substantially eliminating fluid communication between thehousing interior 70 and the atmosphere 72.

Although the vane 10 is illustrated and described in terms of beingmounted pivotably within the housing 14, the vane 10 could be bendablyattached within the housing 14. In such cases, the vane 10 and/or thehousing 14, or a portion of the vane 10 and/or the housing 14, can beconstructed from a flexible material, allowing the vane 10 to bend abouta vane attachment point. The attachment point can be positioned at anypoint along the vane 10, providing a central vane attachment pointsimilar to the illustrated vane pivot axis 34, or providing a cantileverarrangement where the vane attachment point is near the leading edge 28or trailing edge 30 of the vane 10.

In a preferred embodiment, the leading vane edge 28 and thecorresponding leading housing surface 24 have substantially equal radiiof curvature concentric with the vane pivot axis 34. Similarly, trailingvane edge 30 and the corresponding trailing housing surface 26 havesubstantially equal radii of curvature concentric with the vane pivotaxis 34. Consequently, the leading vane edge 28 and the leading housingsurface 24 can sealingly engage each other, depending upon therotational position of the vane 10. The trailing vane edge 30 and thetrailing housing surface 26 can also sealingly engage each other,depending upon the rotational position of the vane 10. The radii ofcurvature of the vane edges and housing surfaces can vary depending uponthe particular embodiment.

There are an unlimited number of intermediate positions that the vane 10can assume between a fully open position and a fully closed position.The range of rotational movement of the vane 10 is constrained in thefully closed position by the interaction of the leading vane edge 28with the leading housing surface 24. In the fully open position, thevane 10 is constrained by the interaction of the leading vane edge 28with the housing bend intersection point 76 (FIGS. 9, 10 and 14). Thehousing bend 32 provides the advantage of reducing the range ofrotational movement of the vane 10 necessary to assume the fully openposition and the fully closed position. The vane may pivot about 30° inthat embodiment, although it can rotate more or less depending onpreference, keeping in mind that response time is decreased as theamount of rotation is decreased. Additionally, the housing bend 32provides smooth tangential curves to the flow within the flow divertervalve 12. Housing bend 32 is confined substantially to the portion ofthe housing interior 70 near the inlet port 16, minimizing a reducedflow path and a resulting flow impedance to the part of the housinginterior 70 near the inlet port 16. Importantly, the part of the housinginterior 70 near the outlet port 18 does not have a reduced flow pathand accordingly does not have unnecessary flow impedance.

In the illustrated embodiment, the engagement between the leading vaneedge 28 and the leading housing surface 24 is not necessarily identicalin nature to the engagement between the trailing vane edge 30 and thetrailing housing surface 26. The difference between the two engagementsis a result of the asymmetrical configuration of the vane 10 and housing14 about the vane pivot axis 34. As the vane 10 rotates between thefully open position, through a plurality of intermediate positions, intothe fully closed position, a leading engagement occurs between theleading vane edge 28 and the leading housing surface 24. A trailingengagement subsequently occurs between the trailing vane edge 30 and thetrailing housing surface 26 as rotation of the vane 10 continues. In theillustrated embodiment, the leading and trailing engagements do notoccur simultaneously as the vane 10 rotates. Additionally, the durationof the leading and trailing engagements is not equal as the vanerotates. The natures of the seals of the leading and trailingengagements are not identical during rotation of the vane 10 and/or whenthe vane 10 is stationary in a fully or partially sealed intermediate orfully closed position.

For example, in the illustrated embodiment shown in FIG. 13, the leadingengagement occurs prior to the trailing engagement as the vane 10rotates from the fully open position into the fully closed position,and/or any number of intermediate positions. There is a plurality ofpartially sealed intermediate positions of the vane 10. These positionsare described by a partial seal, provided by the leading engagementbetween the leading vane edge 28 and the leading housing surface 24,while at the same time no seal is provided between the trailing vaneedge 30 and the trailing housing surface 26. Similarly, as the vane 10rotates in an opposite direction from the fully closed position to thefully open position, it passes through the plurality of partially sealedintermediate positions where the trailing engagement between thetrailing vane edge 30 and the trailing housing surface 26 does notoccur. Alternate embodiments allow the leading and trailing engagementsto occur simultaneously, or allow the trailing engagement to occur whilethe leading engagement does not.

In the illustrated embodiment of FIGS. 4-16, the surface area of boththe leading vane edge 28 and the corresponding leading housing surface24 is greater than the surface area of both the trailing vane edge 30and the corresponding trailing housing surface 26. Additionally, thedifference between the radius of curvature of the leading vane edge 28and the leading housing surface 24 is equal to the difference betweenthe radius of curvature of the trailing vane edge 30 and the trailinghousing surface 26. As a result, when the vane 10 is in the fully closedposition or a substantially closed position, the seal of the leadingengagement is greater than the seal of the trailing engagement. It isunderstood that the natures of the seals can be adjusted by varying thesurface areas and/or the radii of curvature of the vane edges andhousing surfaces. For example, the radii of curvature of the vane edgescan be 20, while the radii of curvature of the housing surfaces can be20.2. An exemplary means of adjusting the surface area of the leadingvane edge 28 is by increasing or decreasing the distance between theleading vane corners 64 (FIGS. 6-7). The surface area of the trailingvane edge 30 can likewise be adjusted by varying the distance betweenthe trailing vane corners 66.

The vane 10 can be positioned in the housing 14 in the open position(FIG. 14), the closed position (FIG. 15) and the plurality ofintermediate positions, e.g., as shown in FIG. 16. In a preferredembodiment, the leading housing surface 24 and the trailing housingsurface 26 are shaped to receive the leading vane edge 28 and thetrailing vane edge 30, respectively, when the vane 10 is rotated aboutthe vane pivot axis 34 into the closed position. Additionally, the radiiof curvature of the leading housing surface 24 and the trailing housingsurface 26 can be slightly larger than the respective radii of curvatureof the leading-vane edge 28 and the trailing vane edge 30. Such anarrangement provides a sufficient seal in the closed position, whileallowing rotation of the vane 10 without excessive friction. The leadinghousing surface 24 and/or the trailing housing surface 26 can contain aleading ledge 86 and/or a trailing ledge 88 to contact the vane 10 whenthe vane 10 is rotated into a fully closed position. FIG. 14A shows theleading housing surface 24 and the trailing housing surface 26 ingreater detail, including the leading ledge 86 and the trailing ledge88. The vane pivot axis 34 is illustrated at a position equidistant fromthe leading vane edge 28 and the trailing vane edge 30. However, thevane pivot axis 34 may be located at various positions between theleading vane edge 28 and the trailing vane edge 30.

The housing 14 and vane 10 are configured such that the blower or flowgenerator 22 is not choked, regardless of the position of the vane 10,which means that the flow through and from the blower is not stopped orsignificantly slowed, e.g., when the vane 10 is in any position. This isin sharp contrast to the cammed valve member disclosed in U.S. patentapplication Ser. No. 09/598,053, which can choke the blower while theapparatus is in the expiration mode. Since the vane 10 does not causechoking of the blower 22, regardless of its position, the speed andresponse time when shifting from the expiration phase to the inspirationphase can be made faster, thereby improving patient comfort anddecreasing power consumption. Stated differently, the blower 22 remainssubstantially unchoked as the vane 10 moves between the open and closedpositions. In another sense, it can be said that the blower is notchoked, at least in part, because the flow capacity of the housing 14downstream of the vane 10 is at least substantially equal to flowcapacity upstream of the vane 10, regardless of the position of the vane10. Because the flow created by the blower 22 passes to the outlet portand/or the exhaust port during all positions of the vane 10, the blower22 remains substantially unchoked. Moreover, flow continues through theblower itself regardless of the position of the vane 10.

Turbulence can be associated with eddying motion of fluid. The vane 10is shaped to minimize flow turbulence generated by interactions betweenthe leading vane edge 28 and the trailing vane edge 30 with the flow 40from the inlet port 16. Accordingly, the shape of the vane 10 reducesnoise, pressure fluctuations, and flow fluctuations associated with flowturbulence. Additionally, the radiused leading vane corners 64 andtrailing vane corners 66 (FIGS. 6-7) reduce the generation of flowseparation associated with turbulence. The vane 10 and the housing 14are configured to minimize pressure fluctuations and flow fluctuations,especially in flow 42 to the outlet port 18. In the closed position,leading vane edge 28 and trailing vane edge 30 are flush with leadinghousing surface 24 and trailing housing surface 26, respectively.Turbulence is minimized by the smooth tangential curves of the housing14, and also by ensuring that the vane 10 has an angle to flow 40 fromthe inlet port 16 not exceeding approximately 15°-25° (except whencompletely shutting off flow 42 to the outlet port 18 in the fully openposition). Preferably, the vane 10 has an angle to flow 40 from theinlet port 16 not exceeding 20°.

In operation, flow generator 22 provides a flow of air or breathable gasto the flow diverter valve 12 via the inlet port 16. The vane 10variably diverts the flow 40 from the inlet port 16 to the exhaust port20 and/or the outlet port 18. The flow 42 diverted to the outlet port 18is conducted to the patient mask 54 via the conduit 52. The vane 10 iscaused to move rotatably about the vane pivot axis 34 within a definedrange by the rotary actuator 58 (FIG. 4). A servo motor, preferablyincorporating a sensor indicative of the angular position of the vanepivot axis 34, can be used as the rotary actuator 58. Pressure feedbackloops used for servo control of the position of the vane 10automatically compensate for any pressure changes due to variation influid viscosity caused by temperature, humidity, or gas compositionchanges. The pressures used in the pressure feedback loops can be takenfrom the flow meter 50, or from the inlet port 16 and the outlet port18, depending upon the particular embodiment of the ventilatoryassistance apparatus 11.

The housing bend 32 provides the benefit of a smaller rotational rangeof the vane 10, resulting in reduced time necessary for the vane 10 torotate about the vane pivot axis 34 between the open position and theclosed position. In one embodiment, the range of vane rotation isgenerally within approximately 25°-35°, preferably 30°, providing areduced response time compared to a larger range of vane rotation.However, the housing bend 32 and the housing bend intersection point 76can be designed to vary the rotational range of the vane 10. Forexample, the radius of curvature of the housing bend 32 can be varied,in addition to varying the distance between the housing bendintersection point 76 and the leading housing surface 24. The angulardistance between the housing surface 24 and the housing bend 32, asmeasured from the vane pivot axis 34, can thereby be reduced.Additionally, the dimensions of the vane 10, such as the radii ofcurvature of the vane edges and the distance between the leading vanecorners 64, can be varied to affect the rotational range of the vane 10constrained by the housing bend 32.

It is preferable to provide a low impedance flow path between the inletport 16 and the outlet port 18. Therefore, the housing bend 32 isconfigured to allow passage of the flow 40 from the inlet port 16 to theoutlet port 18 without excessive impedance to flow. The housing bend 32is also configured to present smooth tangential curves along the flowpath between the inlet port 16 and the outlet port 18, thereby providinga low impedance path from the inlet port 16 to the outlet port 18, whileproviding the benefit of reduced rotation of the vane 10 about the vanepivot axis 34.

The shape of the housing 14, in cooperation with the housing bend 32,can also be configured to direct undiverted flow 40 from the inlet port16 to the outlet port 18, the exhaust port 20, or a combination of theoutlet port 18 and the exhaust port 20. In the embodiment of FIGS. 4-16,the housing bend 32 partially directs the flow 40 from the inlet port 16towards the exhaust port 20 when the vane 10 is at least partially open.

As the vane 10 is rotated to variably divert the flow 40 from the inletport 16 to the outlet port 18, the flow diverter valve 12 operatestypically in an inspiratory and/or an expiratory capacity. Therotational position of the vane 10 associated with a particular pressureand/or flow rate at the outlet port 18 is dependent upon pressure and/orflow rate at the inlet port 16. An outlet pressure and/or flow rateassociated with either inspiratory or expiratory operation of the flowdiverter valve 12 depends upon individual pressures determined for apatient either by a doctor or by using an autosetting machine inaccordance with patient need. However, in the fully open position,substantially none of the flow 40 from the inlet port 16 is diverted tothe outlet port 18 and ultimately to the patient mask 54. This zero flowcondition corresponds to an EPAP level of 0 cm H₂O. In practice, an EPAPlevel of 0 cm H₂O is not used for normal treatment. Rather, the EPAPlevel is approximately 2-12 cm H₂O, and preferably 1-5 cm of H₂O.However, this is generally a clinical issue and not limited by thedesign of the flow diverter valve 12.

Generally, for the expiratory phase of the patient respiratory cycle,the vane 10 is rotated into a plurality of intermediate positions nearthe fully open position, to provide a substantially smaller amount offlow 42 to the outlet port 18. Additionally, the vane 10 provides a lowimpedance path for exhaled back flow 44 to the atmosphere 72. Thiscondition corresponds to an EPAP level of approximately 2-12 cm H₂O, andpreferably 1-5 cm H₂O. For the inspiratory phase of the patientrespiratory cycle, the vane 10 is rotated into the closed position or aplurality of intermediate positions near the fully closed position. Thiscondition results in the vane 10 diverting a substantially larger amountof the flow from the flow generator 22 to the patient, corresponding toan IPAP level of approximately 15-30 cm H₂O.

FIG. 14 illustrates the flow diverter valve 12 with the vane 10 rotatedabout the vane pivot axis 34 into the open position, e.g., a ventingposition. The vane 10 is pivotably rotated about the vane pivot axis 34to divert the flow 40 from the inlet port 16 to the exhaust port 20. Inparticular, while venting the flow 40 from the inlet port 16 to theatmosphere, the vane 10 protrudes into a flow path between the inletport 16 and the outlet port 18, the protrusion limited by abutment withthe housing bend 32. The position of the vane pivot axis 34 along thevane 10 allows a low impedance path for flow on both sides of the vane10 when the vane 10 is in a non-closed position, i.e., the flow divertervalve 12 can exhaust flow 40 from the inlet port 16 to the atmosphere72, while simultaneously exhausting exhaled back flow 44 from thepatient mask via the outlet port 18 to the atmosphere 72.

During operation in the open position, a low positive pressure occurs atthe outlet port 18. The illustrated embodiment is shown in FIG. 14 withthe leading vane edge 28 contacting the housing bend 32. Even with suchcontact between the vane 10 and the housing bend 32, a substantially lowportion of flow 40 from the inlet port 16 can flow to the outlet port18. A seal or gasket (not shown) fitted to either the housing 14 or thevane 10 can alternatively be used to ensure zero flow to the outlet port18. However, zero flow to the outlet port 18 is not generally usedduring patient treatment. In practice, substantially open positions ofthe vane 10 nearly contacting housing bend 32 represent a positivepressure at the outlet port 18 of approximately 2-12 cm H₂O, andpreferably 1-5 cm H₂O. Such a pressure is typically associated with theexpiratory phase of the respiration cycle. In this open position, amajority of the flow 40 from the inlet port 16 is diverted to theexhaust port 20 and out to the atmosphere 72. Additionally, the vane 10provides a low impedance exhalation path via the exhaust port 20 for theback flow 44 from the outlet port 18, so the back flow 44 exhaled by thepatient at the patient mask 54 can be vented to atmosphere withoutpatient discomfort.

FIG. 15 illustrates the flow diverter valve 12 with the vane 10 rotatedabout the vane pivot axis 34 into a fully closed position, whereby theair or breathable gas diverted from the inlet port 16 to the outlet port18 is maximized. This closed position represents the maximum pressure atthe outlet port 18, typically 20-30 cm H₂O, and preferably 15-30 cm H₂O,for CPAP treatment, and is generally used during an inspiratory phase ofthe respiration cycle. The leading housing surface 24 and the trailinghousing surface 26 can be fitted with a seal or gasket (not shown) tosealingly engage the leading vane edge 28 and the trailing vane edge 30when the vane 10 is moved into the fully closed position. Alternativelyand/or additionally, the vane 10 can be fitted with a seal or gasket(not shown) to sealingly engage the housing surfaces. Such a seal orgasket could provide complete diversion of the flow 40 from the inletport 16 in the fully closed position, but is generally not necessaryduring patient treatment.

The leading housing surface 24 can be shaped to provide the leadingledge 86 (FIG. 14A) that protrudes into the exhaust port towards thevane pivot axis 34, so as to contact the lower leading vane corner 64when the vane 10 is rotated into the fully closed position. The trailinghousing surface 26 can similarly be shaped with the trailing ledge 88 tocontact the upper trailing vane corner 66 when the vane 10 is rotatedinto the fully closed position. Such ledges can provide an abutment forthe vane 10, as well as improved sealing between the vane edges and thehousing surfaces without unnecessary impediment to the rotation of thevane 10.

In the closed position of the illustrated embodiment, the vane 10 formsa portion of a passageway leading from the inlet port 16 to the outletport 18 and diverts nearly all of the flow 40 from the inlet port 16 tothe outlet port 18. The leading vane edge 28 and trailing vane edge 30can engage the leading housing surface 24 and trailing housing surface26, respectively, in the closed position. This closed positionengagement between the leading vane edge 28 and trailing vane edge 30,and the leading housing surface 24 and trailing housing surface 26,minimizes leakage of the flow 40 from the inlet port 16 past the vane 10into the exhaust port 20. Alternatively, the radii of curvature of theleading vane edge 28 and the trailing vane edges 30, and/or the radii ofcurvature of the leading housing surface 24 and the trailing housingsurface 26, can be chosen such that the leading vane edge 28 and thetrailing vane edge 30 nearly contact the leading housing surface 24 andthe trailing housing surface 26, respectively, without touching them. Itis desirable to allow rotation of the vane 10 without unnecessaryimpediment, allowing a reduced response time necessary for the vane 10to change position and decreased power requirements for the rotaryactuator 58.

By controlling the rotation of the vane 10 via pressure feedback loops(known in the art), different output treatment pressures can be obtainedfor a given constant pressure at the inlet port 16, as required by thepatient. A range of output pressures at the outlet port 18, to betransmitted via the conduit 52 to the patient mask 54, can beappropriately selected for implementation of CPAP. Higher inspiratorypressures generally correspond with the vane 10 being rotated into asubstantially closed position, as illustrated in FIG. 15, whereby theflow diverter valve 12 diverts a majority of the flow 40 from the inletport 16 to the outlet port 18. Additionally, the vane 10 can be rotatedinto a partially closed and/or partially opened intermediate positionduring IPAP, if a lower inspiratory pressure is desired. The position ofthe vane 10 chosen depends upon the pressure feedback loops used forservo control of the rotary actuator 58. The open position, or anintermediate position, of the vane 10 allows venting of the flow 40 fromthe inlet port 16 to the atmosphere 72 via the exhaust port 20.Accordingly, the pressures at the outlet port 18 obtained with the vane110 in the plurality of intermediate positions are lower than thepressures obtained when the vane 10 is in a substantially closedposition.

An expiratory positive airway pressure of 0 cm H₂O is generally not usedfor normal patient treatment. Therefore, it is not always necessary toobtain an outlet port pressure and/or flow of zero by diverting all ofthe flow 40 from the inlet port 16 to the exhaust port 20. Accordingly,there is no absolute need for the leading vane edge 28 to contact thehousing bend 32 in the open position, and a smaller, lighter vane with areduced response time can be used. However, it is understood that thevane 10 could be configured so that the vane surface 28 contacts thehousing bend 32 in the open position, if necessary.

Turbulence can be caused by flow separation, which can arise whensurfaces of the housing 14 or the vane 10 are presented to the flow 40from the inlet port 16 at angles greater than approximately 15°-25°.FIG. 16 illustrates the flow diverter valve 12 with the vane 10 placedin an intermediate position both partially diverting the flow 40 fromthe inlet port 16 to the outlet port 18 and partially venting the flow40 from the inlet port 16 to the exhaust port 20. Exhaled back flow 44from the outlet port 18 is vented to the atmosphere 72 via exhaust port20 in the illustrated intermediate position of the vane 10. Turbulencecaused by flow separation 36 occurs within the exhaust port 20. However,the vane 10 confines flow separation 36 to the exhaust port 20 of theflow diverter valve 12. Disadvantages including noise and flowfluctuation associated with flow separation 36 are accordingly confinedto the exhaust port 20, isolated away from the flow 42 to the outletport 18. Importantly, turbulence and fluctuations of flow within theflow meter 50 are minimized. This provides the benefit of improved flowdetermination accuracy and/or speed, and increased patient comfort andcompliance with treatment.

The housing bend 32 provides an additional benefit that turbulence inthe flow 42 to the outlet port 18 is minimized when the vane 10 is inthe open or intermediate positions. The flow 40 from the inlet port 16that flows between the leading vane edge 28 and the housing bend 32 inthe open or intermediate positions is presented with surfaces at nogreater than approximately 15°-25° to the flow 40 from the inlet port16, substantially eliminating flow separation. As illustrated in FIG.16, the housing bend 32 redirects a portion of the flow 40 from theinlet port 16 in a direction approximately coplanar with the vane 10,reducing the angle of incidence between the flow 40 from the inlet port16 and the vane 10. The reduced angle of incidence minimizes separationof the flow 40 and resultant turbulence on a side of the vane 10 exposedto the outlet port 18, minimizing noise and pressure fluctuationsassociated with flow separation in the flow 42 to the outlet port 18.

Minimizing flow fluctuations is significant because flow fluctuationsintroduce disadvantages such as noise into the calculations used todetermine flow. Accounting for any flow fluctuation noise in the flow 42to the outlet port 18 during flow calculation requires extra signalprocessing as well as extra time. Therefore, minimizing flowfluctuations provides advantages including reduced flow calculationcircuitry and reduced response time, particularly important in thepressure feedback loops used to control the position of the vane 10.

The materials of the housing 14 can be constructed from castable metalssuch as stainless steel, aluminum or magnesium as well as injectionmoldable polymers such as polycarbonate, polypropylene, glass reinforcednylon or epoxy, or any other suitable medical grade plastic. The vane 10has similar requirements, with the understanding that it may bepreferable to construct the vane 10 with materials that are lightweight.Such preference depends upon the desired response speed and thecharacteristics of the rotary actuator 58 used to rotate the vane 10.The surface texture of the housing interior 70 and the vane 10 ispreferably smooth to reduce flow impedance. Additionally, the texturesof the housing interior 70, the lower vane edge 80 and the upper vaneedge 82 that come in contact with the housing interior 70 are preferablysmooth to provide sufficient seals while reducing friction, wear,impeded movement of the vane 10, and contact pressure necessary toprovide the sufficient seals.

While preferred embodiments of the invention have been described withreference to specific examples, it will be appreciated by those skilledin the art that the invention may be embodied in many other forms.

For example, FIGS. 17-19 illustrate the flow diverter valve 12 of FIGS.4-16 in an alternative embodiment. In particular, an exhaust port 220 ofa flow diverter valve 212 is disposed in line with flow 240 from aninlet port 216, and an outlet port 218 is disposed at an angle greaterthan zero to the flow 240 from the inlet port 216. Additionally, ahousing 214 with a housing bend 232, and a vane 210 are disposed so thatwhen in an open position, illustrated in FIG. 17, the vane 210 does notdivert the flow 240 from the inlet port 216 in a direction other thanthe original direction of the flow 240 from the inlet port 216. The vane210 is shown with a first side vane surface 260 and a second side vanesurface 262 with radii of curvature that are approximately equal. Whilenot illustrated, it is understood that the radius of curvature of thefirst side vane surface 260 could be larger than the radius of curvatureof the second side vane surface 262. Additionally, it is understood thatthe vane 210 could be configured to contact the housing 214 or thehousing bend 232 in the open position, if necessary to provide completediversion of the flow 240 from the inlet port 216 to the atmosphere 272.In a closed position, illustrated in FIG. 18, the vane 210 diverts amajority of the flow 240 from the inlet port 216 to the outlet port 218.

FIG. 19 illustrates the flow diverter valve 212 with the vane 210 placedin a position both partially diverting the flow 240 from the inlet port216 to the outlet vent 218 and partially venting the flow 240 from theinlet port 216 to the exhaust port 220. As illustrated, flow separation236 occurs, caused by a leading portion of the vane 210 protruding intoundiverted flow 240 from the inlet port 216 at an angle greater thanapproximately 15-25° to the flow 240 from the inlet port 216. The flowseparation 236 does not occur on a side of the vane 210 facing theoutlet port 218.

The flow separation 236 occurs on a side of the vane 210 facing theexhaust port 220. Accordingly, turbulence caused by the flow separation236 is confined to the exhaust port 220, isolated from flow 242 divertedto the outlet port 218. Fluctuations in the flow 242 to the outlet port218 are thereby minimized. Additionally, the exhaust port 220 can befitted with a filter or muffler component (not shown), furtherminimizing noise produced by the flow diverter valve 212.

FIG. 20 illustrates the flow diverter valve 12 of FIGS. 4-16 in yetanother embodiment. In this embodiment, an outlet port 318 of a flowdiverter valve 312 is disposed in line with flow 340 from an inlet port316, and an exhaust port 320 is disposed at an angle greater than zeroto the flow 340 from the inlet port 316. Additionally, a housing 314 anda vane 310 are disposed so that when in the closed position, the vane310 and the housing 314 do not substantially alter the direction of theflow 340 from the inlet port 316. In the open position, the vane 310protrudes into the flow 340 from the inlet port 316, diverting at leasta portion of the flow 340 from the inlet port 316 into the exhaust port320 where it is vented to the atmosphere 372.

It can thus be appreciated that the objectives of the present inventionhave been fully and effectively accomplished. The foregoing specificembodiments have been provided to illustrate principles of the presentinvention and are not intended to be limiting. To the contrary, thepresent invention is intended to encompass all modification,alterations, and substitutions within the spirit and scope consistentwith the principles and novel features disclosed in any fashion herein.

1. A valve assembly for use in a ventilator, the valve assemblycomprising a housing and a rotatable vane for directing the flow of airwithin the housing, the housing having an inlet port for receiving aflow of pressurized air from a blower, an outlet port for delivering airto a patient interface and an exhaust port, the vane being rotatablebetween a first angular position and a second angular position withoutchoking the blower, wherein: (i) in the first angular positionsubstantially all of the flow of air received at the inlet port isdirected by the vane to the exhaust port, (ii) in the second angularposition substantially all of the flow of air received at the inlet portis directed by the vane to the outlet port, (iii) in angular positionsintermediate of the first and second angular positions, a fraction ofthe flow of air received at the inlet port is directed by the vane tothe exhaust port and the complementary fraction of the flow of airreceived at the inlet port is directed by the vane to the outlet port.2. The valve assembly of claim 1, wherein an arc through which the vanemoves between the first and second angular positions is approximately 30degrees.
 3. The valve assembly of claim 1, wherein the vane forms aportion of a passageway between the inlet port and the outlet port whenin the second angular position.
 4. The valve assembly of claim 1,wherein the vane can selectively direct undiverted flow from the inletport to at least one of the exhaust port and the outlet port when thevane is between the first angular position and the second angularposition.
 5. A ventilatory assistance apparatus, comprising: a flowgenerator; and a flow diverter valve in communication with the flowgenerator, the flow diverter valve including a housing defining an inletport, an outlet port and an exhaust port positioned between the inletport and the outlet port and configured to exhaust at least one of flowfrom the inlet port and back flow from the outlet port, and a vanemoveable between an open position and a closed position, wherein: thevane can selectively protrude into the flow from the inlet port andthereby variably divert the flow from the inlet port to at least one ofthe exhaust port and the outlet port, and the vane forms a portion of apassage leading to the outlet port when in the closed position.
 6. Theapparatus of claim 5, wherein the housing includes a housing bend thatextends towards the vane into the flow from the inlet port.
 7. Theapparatus of claim 6, wherein the housing bend defines a stop for thevane in the open position.
 8. The apparatus of claim 5, wherein thehousing includes at least one of a leading housing ledge and a trailinghousing ledge that defines a stop for the vane in the closed position.9. The apparatus of claim 5, wherein the housing has smooth tangentiallycurved inside surfaces with a low angle of incidence to the flow fromthe inlet port.
 10. The apparatus of claim 5, further comprising a flowmeter downstream of the flow diverter valve.
 11. The apparatus of claim5, further comprising an apparatus body including a side wall with anopening aligned with the exhaust port.
 12. The apparatus of claim 5,wherein the flow generator includes a blower that remains substantiallyunchoked as the vane moves between the open position and the closedposition.
 13. A flow diverter valve, comprising: a housing defining aninlet port and an outlet port; an exhaust port positioned between theinlet and outlet ports; and a vane moveable between an open position anda closed position, wherein: the vane can selectively protrude into theflow from the inlet port and thereby variably divert the flow from theinlet port to at least one of the exhaust port and the outlet port, andthe vane forms a portion of a passage leading to the outlet port when inthe closed position.
 14. The flow diverter valve of claim 13, whereinthe housing includes at least one of a leading housing ledge and atrailing housing ledge that defines a stop for the vane in the closedposition.
 15. The flow diverter valve of claim 13, wherein the vane ispivotable between the open position and the closed position.
 16. Theflow diverter valve of claim 13, wherein the vane comprises a flexiblematerial that can bend, the vane bendable between the open position andthe closed position.
 17. The flow diverter valve of claim 13, whereinthe housing includes a straight inlet port flow path from the inlet portto the exhaust port directing a majority of undiverted flow from theinlet port to the exhaust port.
 18. The flow diverter valve of claim 13,wherein the housing includes a straight inlet port flow path from theinlet port to the outlet port directing a majority of undiverted flowfrom the inlet port to the outlet port.
 19. The flow diverter valve ofclaim 13, wherein the vane has a first side surface and a second sidesurface with a first radius of curvature and a second radius ofcurvature.
 20. The flow diverter valve of claim 19, wherein the firstradius of curvature is equal to the second radius of curvature.
 21. Theflow diverter valve of claim 19, wherein the first radius of curvatureis greater than the second radius of curvature.
 22. The flow divertervalve of claim 19, wherein the first radius of curvature is less thanthe second radius of curvature.
 23. The flow diverter valve of claim 22,wherein the first radius of curvature is approximately 120 mm and thesecond radius of curvature is approximately 200 mm.
 24. A CPAPapparatus, comprising: a flow generator; and a flow diverter valve incommunication with the flow generator, the flow diverter valve includinga housing defining an inlet port, an outlet port and an exhaust portpositioned between the inlet port and the outlet port and configured toexhaust at least one of flow from the inlet port and back flow from theoutlet port, and a vane moveable between an open position and a closedposition, wherein the vane can selectively admit undiverted flow fromthe inlet port to at least one of the exhaust port and the outlet portwhen the vane is in the open position.
 25. The apparatus of claim 24,wherein the flow generator includes a blower that remains substantiallyunchoked as the vane moves between the open position and the closedposition.
 26. A flow diverter valve, comprising: a housing defining aninlet port and an outlet port; an exhaust port positioned between theinlet and outlet ports; and a vane moveable between an open position anda closed position, wherein the vane can selectively admit undivertedflow from the inlet port to at least one of the exhaust port and theoutlet port when the vane is in the open position.
 27. The flow divertervalve of claim 26, wherein flow capacity of the housing downstream ofthe vane is at least substantially equal to flow capacity upstream ofthe vane, regardless of whether the vane is in the open position or theclosed position.